This invention pertains to sustained release of bioactive polypeptides.
Many drug delivery systems have been developed, tested and utilized for the controlled in vivo release of pharmaceutical compositions. For example, polyesters such as poly (DL-lactic acid), poly (glycolic acid), poly (.sub..epsilon. -caprolactone) and various other copolymers have been used to release biologically active molecules such as progesterone; these have been in the form of microcapsules, films, or rods (Pitt C G, Marks, T A, and Schindler, A. 1980). Upon implantation of the polymer/therapeutic agent composition, for example subcutaneously or intramuscularly, the therapeutic agent is released over a specific period of time. Such biocompatible biodegradable polymeric systems are designed to permit the entrapped therapeutic agent to diffuse from the polymer matrix. Upon release of the therapeutic agent, the polymer is degraded in vivo, obviating surgical removal of the implant. Although the factors that contribute to polymer degradation are not well understood, it is believed that such degradation for polyesters may be regulated by the accessibility of ester linkages to non-enzymatic autocatalytic hydrolysis of the polymeric components.
Several EPO publications and U.S. patents have addressed issues of polymer matrix design and its role in regulating the rate and extent of release of therapeutic agents in vivo.
For example, Deluca (EPO Publication 0 467 389 A2/Univ of Kentucky) describes a physical interaction between a hydrophobic biodegradable polymer and a protein or polypeptide. The composition formed was a mixture of a therapeutic agent and a hydrophobic polymer that sustained its diffusional release from the matrix after introduction into a subject.
Hutchinson (U.S. Pat. No. 4,767,628/ICI) controlled the release of a therapeutic agent by uniform dispersion in a polymeric device. It is stated that this formulation provides for controlled continuous release by the overlap of two phases: first, a diffusion-dependent leaching of the drug from the surface of the formulation; and second, releasing by aqueous channels induced by degradation of the polymer.